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A common cause of a jumpy and inaccurate temperature gauge needle is a loose ground or a short circuit in the instrument cluster. However, because the e30 has a real temperature sender that isn’t buffered or averaged out it’s prone to some erratic movement as warmer or colder coolant passes through the thermostat housing.

The jumpy needle can indicate a loose ground in the cluster, a fault in the wiring harness or might even indicate a cooling issue such a failing head gasket. I swapped in a performance radiator because I wanted to ensure maximum cooling but to solve the jumpy needle I needed to check the other possibilities.

Above: Generally considered ‘normal’ e30 running temperature.

When troubleshooting anything I always start with the easiest, simplest solution just in case it proves correct. In this case that’s the ground on the temperature VDO gauge. I decided to check it, and do a few other cosmetic things on the cluster while I was in there:

Find and tighten the ground nut on for the temperature gauge.

Replace the missing Anti-Lock bulb to help further diagnose my non-functioning ABS.

Replace the plastic gauge rings the PO added.

Touch up the red needles the PO painted.

Temperature Needle Ground Nut

After removing the cluster I used a 7mm screwdriver socket bit that I got with a euro toolkit to tighten the nut. It’s not a common tool so you may have to buy a thin wall socket just for this job. On my cluster it appears that someone already tightened the fuel gauge nut but used some pliers which damaged the plastic around the nut. The PO is always the worst person.

Above: The brass temp gauge ground nut is next to the blue plug.

I used light pressure to tighten the nut until it felt about as tight as the fuel gauge nut. The cluster is mostly plastic so over tightening would be a terrible thing. I’m happy to report that it looks like this has fixed my jumpy temperature gauge entirely.

Anti-Lock Bulb

Replacing the bulb is straight forward. Now I need to diagnose my non-functioning ABS which is causing the bulb to light. In the above picture the anti-lock bulb socket is just a plastic hole. The bulb is actually attached to the harness. More on that in another blog entry.

Gauge Rings and Needles

The previous owner put ABS plastic rings around the instrument gauges and even though they are kind of ricey I admit that I’ve grown fond of them. I ordered two sets of real metal rings from Bavarian Restoration (I ordered mine via R3vlimited): polished aluminum and brushed metal. The brushed metal appeared to bright to me so I opted for the polished aluminum.

Above: Polished vs matte cluster rings.

Fitment of the Bavarian Restoration rings was excellent and required only firm, even pressure to snap into the cluster. While I had the cluster I also used some red Sharpie to touch up the PO’s sloppy paint job on the gauge needles.